Answer

System modelling

System modelling is the process of developing a mathematical, logical or computer representation of a real system so that its structure, behaviour and interactions can be studied. A model contains the important entities, variables, relationships, inputs and outputs of the actual system.

Continuous vs. discrete-event systems

Continuous system	Discrete-event system
State variables change continuously with time.	State changes occur at specific points/events.
Usually represented using differential/algebraic equations.	Usually represented using event logic, state transitions and queues.
Time advances continuously.	System state changes when an event occurs.
Example: temperature variation, fluid level, motor speed.	Example: arrival/departure of jobs, machine failure/repair, production-line queues.

In short: Continuous simulation tracks continuously varying quantities, whereas discrete-event simulation tracks changes caused by individual events.